// <img id="img" />

// const el = document.getElementById('img') as HTMLImageElement
// el.src = "url地址"


class Person{ }

class Student extends Person{
    studying() {
        console.log('studying');
        
    }
}

function sayHello(p: Person) {
    (p as Student).studying()
}
const stu = new Student()
sayHello(stu)